Adhesive composition and adhesive film

ABSTRACT

An adhesive composition which is reduced in gas generation upon heating (has low hygroscopicity), has high alkali resistance, has heat resistance of 200° C. or higher, and can be easily removed with a stripping liquid; and an adhesive film made with the adhesive composition. The adhesive composition is prepared using, at least as a major ingredient, an acrylic polymer produced from (a) styrene, (b) a (meth)acrylic ester monomer containing a cyclic skeleton, and (c) an alkyl (meth)acrylate monomer. The adhesive film has an adhesive composition layer formed from this adhesive composition.

TECHNICAL FIELD

The present invention relates to an adhesive composition, andparticularly relates to an adhesive composition for temporarily fixing asheet or a protective substrate on a product in order to hold andprotect the product in steps of high-precision processing, for example,in grinding optical products and semiconductor products such assemiconductor wafers, and an adhesive film.

BACKGROUND ART

Conventionally, tacky adhesion sheets have been used for surfaceprotection and damage prevention of the products when optical parts suchas lenses, and semiconductor products such as semiconductor wafers aresubjected to high-precision processing in optical industry,semiconductor industry, and the like. For example, in production stepsof semiconductor chips, the semiconductor chip is produced by: slicinghighly purified silicon single crystals or the like to give a wafer;incorporating an integrated circuit by etching of a certain circuitpattern such as IC on the wafer surface; grinding the back face of theresulting semiconductor wafer by way of a grinder to reduce thethickness of the semiconductor wafer to about 100 to 600 μm; and dicecutting the semiconductor wafer following grinding to a predeterminedthickness, thereby forming a chip.

According to the production of the semiconductor chip described above,the semiconductor wafer itself has a small thickness, and is fragile. Inaddition, because of the relief structure of the circuit pattern, thewafer is liable to be damaged when external force is applied duringcarrying to the grinding step or the dice cutting step. Additionally, inorder to remove the polishing dust generated in the polish processingstep, or to eliminate the heat generated during polishing, the grindingprocess is carried out while washing the back face of the semiconductorwafer with purified water. Therefore, it is necessary to prevent thecircuit pattern face from being contaminated by the rinse water and thelike yielded in the washing. Accordingly, in order to protect thecircuit pattern face of the semiconductor wafer, and concurrently toprevent damage of the semiconductor wafer, the grinding operation hasbeen carried out with a tacky adhesion sheet for processing attachedonto the circuit pattern face. Moreover, in the dice cutting, aprotective sheet is attached on the back face side of the wafer, and thedice cutting is conducted in a state with the wafer being adhered andfixed. The thus obtained chip is picked up by sticking from the filmsubstrate side with a needle, and then fixed on a die pad.

Known exemplary tacky adhesion sheets for high-precision processinginclude, e.g., those having an adhesive layer formed from an adhesivecomposition provided on a substrate sheet of polyethylene terephthalate(PET), polyethylene (PE), polypropylene (PP), an ethylene-vinyl acetatecopolymer (EVA) or the like (for example, Patent Document 1, PatentDocument 2, Patent Document 3).

Furthermore, a constitution in which a protective substrate produced byimpregnating a ladder type silicone oligomer into an aluminumnitride-boron nitride sintered compact with pore is used in place of theprotective tape, and this protective substrate is adhered to asemiconductor wafer using a thermoplastic film is also disclosed (PatentDocument 4). In addition, a constitution in which a material such asalumina, aluminum nitride, boron nitride or silicon carbide havingsubstantially the same coefficient of thermal expansion as that of thesemiconductor wafer is used as a protective substrate and using athermoplastic resin such as polyimide as an adhesive for adhering theprotective substrate with the semiconductor wafer, a film having athickness of 10 to 100 μm is provided by applying this adhesivecomposition, and a method which includes spin coating of an adhesivecomposition, and drying to give a film having a thickness of no greaterthan 20 μm were proposed (Patent Document 5).

Furthermore, in recent years, as multilayer-wiring of semiconductorelements has progressed, a process in which: a protective substrate isadhered using an adhesive composition on the surface of a semiconductorwafer having a circuit formed thereon; the back face of thesemiconductor wafer is polished; thereafter, the polished face is etchedto give a mirror face; and a circuit on the back face side is formed onthis mirror face has put into practice. In this case, the protectivesubstrate is kept adhered until the circuit on the back face side isformed (Patent Document 6).

Patent Document 1: Japanese Unexamined Patent Application, FirstPublication No. 2003-173993;

Patent Document 2: Japanese Unexamined Patent Application, FirstPublication No. 2001-279208;

Patent Document 3: Japanese Unexamined Patent Application, FirstPublication No. 2003-292931;

Patent Document 4: Japanese Unexamined Patent Application, FirstPublication No. 2002-203821;

Patent Document 5: Japanese Unexamined Patent Application, FirstPublication No. 2001-77304;

Patent Document 6: Japanese Unexamined Patent Application, FirstPublication No. S61-158145;

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The adhesive composition that constitutes the adhesive layer of theprotective tape disclosed in Patent Document 1 or Patent Document 2 isnot resistant to a high temperature as high as 200° C., and is thusproblematic in poor heat resistance. Also, a gas is generated uponheating, leading to inferior adhesion. Moreover, the adhesivecomposition that constitutes the adhesive layer of the protective tapedisclosed in Patent Document 3 is an epoxy resin composition; therefore,there arises a problem of causing peel failure since the epoxy resin ishardened at a high temperature as high as 200° C. to leave residuesafter the removal.

When alumina, aluminum nitride, boron nitride, silicon carbide or thelike is used as the protective substrate (support plate) in place of theprotective tape as disclosed in Patent Document 4 or Patent Document 5,automation of handling and carrying is enabled. However, by way of thethermoplastic film used in adhesion between the protective substrate andthe semiconductor wafer, degassing due to the moisture absorption cannotbe prevented, thereby often leading to adhesion failure.

In addition, not only the grinding of the semiconductor wafer, but themirror finishing process with an etching liquid and the metal filmformation process under a vacuum environment are carried out accordingto the process disclosed in Patent Document 6; therefore, heatresistance, etching resistance, stripping resistance, and crackresistance are required according to the adhesive composition foradhering the protective substrate and the semiconductor wafer. However,this Patent Document 6 does not disclose any specific detail of theadhesive composition.

Moreover, investigation by the present inventors suggested that anacrylic resin material is preferred as an adhesive composition deemed tobe suitable in the aforementioned field, since favorable crackresistance can be achieved. However, even though an adhesive compositionincluding the acrylic material having such an excellent characteristicis used, the following other problems were revealed to occur.

(1) When the adhesive layer and the protective substrate are subjectedto thermo compression bonding, the moisture absorbed by at least theadhesive layer generates a gas, resulting in frothy stripping on theboundary surface of adhesion, whereby adhesion failure is caused.

(2) When the process includes the step of allowing the wafer to be incontact with an alkaline slurry or an alkaline liquid such as analkaline developer, the contact face with the adhesive composition isdeteriorated through peeling, dissolution, dispersion and the like bythe alkaline liquid.

(3) A substance insoluble in the stripping liquid is formed on theadhesive layer after heating at 200° C. or higher, which may bedifficult to remove.

The present invention was made in view of the abovementionedcircumstances, and an object thereof is to provide an adhesivecomposition and an adhesive film which is reduced in gas generation uponheating, has high alkali resistance, has heat resistance of 200° C. orhigher, and can be easily removed with a stripping liquid.

Means for Solving the Problems

The adhesive composition according to a first aspect of the presentinvention includes as a major ingredient, an acrylic polymer producedfrom (a) styrene, (b) a (meth)acrylic ester monomer containing a cyclicskeleton, and (c) an alkyl (meth)acrylate monomer.

The adhesive composition according to a second aspect of the presentinvention is characterized in that the (meth)acrylic ester monomercontaining a cyclic skeleton (b) includes at least (b1) a (meth)acrylicester monomer containing a cyclic skeleton having a substituent on thecyclic skeleton, and (b2) a (meth)acrylic ester monomer containing acyclic skeleton not having a substituent on the cyclic skeleton in theadhesive composition according to the first aspect of the presentinvention.

The adhesive composition according to a third aspect of the presentinvention is characterized in that the acrylic polymer has a carboxylgroup content of no higher than 1.0 mmol/g in the adhesive compositionaccording to the first or the second aspect of the present invention.

The adhesive composition according to a fourth aspect of the presentinvention is characterized in that the adhesive composition according toany one of the first to the third aspects of the present invention is anadhesive composition for adhesion of a protective substrate forhigh-precision processing of a semiconductor wafer used for adhering aprotective substrate for high-precision processing of the semiconductorwafer to the semiconductor wafer.

The adhesive composition according to a fifth aspect of the presentinvention is characterized in that a stripping liquid used for removingthe protective substrate from the semiconductor wafer has a solubilityparameter (SP value) that is approximate to the SP value of the acrylicpolymer in the adhesive composition according to the fourth aspect ofthe present invention.

The adhesive film according to a sixth aspect of the present inventionis characterized by including an adhesive composition layer formed fromat least the adhesive composition according to any one of the first tothe fifth aspects of the present invention on a support film.

In order to solve the foregoing problems, the adhesive compositionaccording to the present invention is characterized by including as amajor ingredient, an acrylic polymer produced from (a) styrene, (b) a(meth)acrylic ester monomer containing a cyclic skeleton, and (c) analkyl (meth)acrylate monomer.

According to the composition of the present invention, heat resistance(not deteriorated even at 200° C.) can be improved by blending theaforementioned styrene (a). It is preferred that the amount of theblended styrene (a) be 30 to 90 parts by mass per 100 parts by mass intotal of the styrene (a), the (meth)acrylic ester monomer containing acyclic skeleton (b), and the alkyl (meth)acrylate monomer (c). Blendingin an amount of no less than 30 parts by mass can achieve efficaciousheat resistance, while blending in an amount of no more than 90 parts bymass can lead to inhibition of decrease in the crack resistance.

By blending the (meth)acrylic ester monomer containing a cyclic skeleton(b), heat resistance can be improved, and the amount of acrylic acidneeded in the polymer can be reduced, whereby attaining favorablestripping property by the stripping liquid can be realized. Althoughcommonly employed stripping liquid can be used as the stripping liquid,a stripping liquid containing PGMEA (propylene glycol monomethyl etheracetate), ethyl acetate, or methyl ethyl ketone as a major ingredient isparticularly preferred in light of the environmental burden andstripping properties. Furthermore, heat resistance can be improved alsoby blending this (meth)acrylic ester monomer containing a cyclicskeleton (b). It is preferred that the amount of the blended(meth)acrylic ester monomer containing a cyclic skeleton (b) be 5 to 60parts by mass per 100 parts by mass in total of the styrene (a), the(meth)acrylic ester monomer containing a cyclic skeleton (b), and thealkyl (meth)acrylate monomer (c). Blending in an amount of no less than5 parts by mass can achieve efficacious heat resistance, while blendingin an amount of no more than 60 parts by mass can lead to inhibition ofdeterioration of the stripping property.

By blending the alkyl (meth)acrylate monomer (c), flexibility and crackresistance of the adhesive layer can be attained. It is preferred thatthe amount of the blended alkyl (meth)acrylate monomer (c) be 10 to 60parts by mass per 100 parts by mass in total of the styrene (a), the(meth)acrylic ester monomer containing a cyclic skeleton (b), and thealkyl (meth)acrylate monomer (c). Efficacious flexibility and crackresistance can be achieved by blending no less than 10 parts by mass,while hygroscopicity and reduction of heat resistance as well as peelfailure can be inhibited by blending no more than 60 parts by mass.

The (meth)acrylic ester monomer containing a cyclic skeleton is amonomer unit derived from a (meth)acrylic ester, and has a structure inwhich a hydrogen atom in the carboxyl group is substituted with a cyclicgroup or an alkyl group having a cyclic group. Alternatively, the(meth)acrylic ester monomer containing a cyclic skeleton is a monomerunit derived from a (meth)acrylic ester, and has a structure in which ahydrogen atom in the carboxyl group is substituted with an alkylolgroup, and further a hydrogen atom in the alkylol group is substitutedwith a cyclic group.

Illustrative examples of the cyclic group include monocyclic groups orpolycyclic groups having an aromatic property such as groups derivedfrom benzene, naphthalene, anthracene and the like by eliminating one ormore hydrogen atom(s), as well as the following aliphatic cyclic groups.The cyclic group may or may not have a substituent on the cyclicskeleton thereof.

Specific examples of such aliphatic cyclic groups include groups derivedfrom monocycloalkane, polycycloalkane such as dicycloalkane,tricycloalkane, tetracycloalkane and the like by eliminating one or morehydrogen atom(s). More specifically, groups derived from monocycloalkanesuch as cyclopentane and cyclohexane, and polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane andtetracyclododecane by eliminating one or more hydrogen atom(s) can beexemplified. In particular, groups derived from cyclohexane ordicyclopentane by eliminating one or more hydrogen atom(s) arepreferred, which may further have a substituent.

When the cyclic group has a substituent on the cyclic skeleton thereof,examples of the substituent include polar groups such as a hydroxylgroup, a carboxyl group, a cyano group and an oxygen atom (═O), andlinear or branched lower alkyl groups having 1 to 4 carbon atoms. Whenthe cyclic group has a substituent on the cyclic skeleton, thesubstituent is preferably the polar group and/or the lower alkyl group.As the polar group, an oxygen atom (═O) is particularly preferred.

As the alkyl group having a cyclic group, an alkyl group having 1 to 12carbon atoms and having the cyclic group described above is preferred.Examples of the (meth)acrylic ester monomer containing a cyclic skeletoninclude cyclohexyl-2-propylacrylate, and the like.

As the alkylol group, an alkylol group having 1 to 4 carbon atoms ispreferred. Examples of such a (meth)acrylic ester monomer containing acyclic skeleton include phenoxyethyl acrylate, phenoxypropyl acrylate,and the like.

The term “aliphatic” referred to in claims and specification of thepresent application is defined to mean a relative concept contrary to“aromatic”, and involves groups, compounds and the like not having anaromatic property. The term “aliphatic cyclic group” indicates amonocyclic group or a polycyclic group not having an aromatic property.The base ring structure of the “aliphatic cyclic group” except for thesubstituent is not limited to a group consisting of carbon atoms andhydrogen atoms (i.e., hydrocarbon group), but is preferably ahydrocarbon group. Also, the “hydrocarbon group” may be either saturatedor unsaturated, but is preferably saturated, in general. Furthermore, apolycyclic group is preferred.

In the adhesive composition of the present invention, (b) an ingredientincluding at least (b1) a (meth)acrylic ester monomer containing acyclic skeleton having a substituent on the cyclic skeleton, and (b2) a(meth)acrylic ester monomer containing a cyclic skeleton not having asubstituent on the cyclic skeleton can be used as the (meth)acrylicester monomer containing a cyclic skeleton (b). By concurrentlyincluding the ingredient (b1) and the ingredient (b2) as the ingredient(b), maintenance of the heat resistance, and improvement of flexibilitycan be both achieved more easily.

The alkyl (meth)acrylate monomer (c) means acrylic long chain alkylesters in which the alkyl group has 15 to 20 carbon atoms, and acrylicalkyl esters in which the alkyl group has 1 to 14 carbon atoms.

Examples of the acrylic long chain alkyl esters in which the alkyl grouphas 15 to 20 carbon atoms can include long chain alkyl esters of acrylicacid or methacrylic acid, in which the alkyl group is a n-pentadecylgroup, n-hexadecyl group, n-heptadecyl group, n-octadecyl group,n-nonadecyl group, or n-eicosyl group. Also, the long chain alkyl groupmay be branched.

As the acrylic alkyl esters in which the alkyl group has 1 to 14 carbonatoms, known ones which have been used in conventional acrylic adhesivescan be exemplified. Typical examples thereof include alkyl esters ofacrylic acid or methacrylic acid in which the alkyl group is a methylgroup, an ethyl group, a propyl group, a butyl group, a 2-ethylhexylgroup, an isooctyl group, an isononyl group, an isodecyl group, adodecyl group, a lauryl group, or a tridecyl group.

In the adhesive composition of the present invention, when the acrylicpolymer produced from the aforementioned ingredients (a), (b), and (c)is obtained, it is desired that the carboxyl group content in thepolymer be no greater than 1.0 mmol/g. When the carboxyl group contentis no greater than 1.0 mmol/g, hygroscopicity can be lowered, wherebyreduction in tacky adhesiveness due to a pseudo-crosslinking effect thatis deemed to result from hydrogen bonds formed between carboxyl groupscan be inhibited. In addition, it was ascertained that alkali resistanceis improved by keeping the carboxyl group content at a low value.Therefore, since deterioration of the adhesive layer is less likely tooccur even though it is in contact with an alkaline liquid, the degreeof freedom of applicable range can be enlarged.

In the adhesive composition of the present invention, the acrylicpolymer has a molecular weight of preferably 5,000 to 500,000, and morepreferably 10,000 to 100,000. When the molecular weight falls withinthis range, flexibility and crack resistance of the formed adhesivelayer can be further efficacious.

In the adhesive composition of the present invention, acrylamide such asdimethyl acrylamide, and morpholine such as acryloylmorpholine may beblended as other additives. By blending these compounds, concurrentimprovement of the heat resistance and adhesiveness can be expected.

To the adhesive composition of the present invention can be furtheradded as desired, miscible additives such as, e.g., an additional resinfor improving the adhesive performances, a plasticizer, an adhesion aid,a stabilizer, a colorant, a surfactant and the like, which are commonlyused, to be included in the range not to deteriorate essential features.

Furthermore, an organic solvent can be appropriately blended in theadhesive composition of the present invention for adjusting theviscosity. Specific examples of such organic solvent include: ketonessuch as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamylketone, and 2-heptanone; polyvalent alcohols and derivatives thereof,such as ethylene glycol, ethylene glycol monoacetate, diethylene glycol,diethylene glycol monoacetate, propylene glycol, propylene glycolmonoacetate, dipropylene glycol or dipropylene glycol monoacetate, ormonomethyl ether, monoethyl ether, monopropyl ether, monobutyl ether ormonophenyl ether thereof; cyclic ethers such as dioxane; and esters suchas methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butylacetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, andethyl ethoxypropanoate. These may be used alone, or in any combinationsof two or more thereof. Particularly, polyvalent alcohols andderivatives thereof such as ethylene glycol, propylene glycol,diethylene glycol, ethylene glycol monoacetate, propylene glycolmonoacetate, diethylene glycol monoacetate, or monomethyl ether,monoethyl ether, monopropyl ether, monobutyl ether or monophenyl etherthereof are preferred. Also, an active agent may be added thereto forimproving uniformity of the film thickness.

The adhesive composition of the present invention realizes an excellenteffect by, in particular, using as an adhesive composition for adhesionof a protective substrate for high-precision processing of semiconductorwafers, which is for use in adhering a protective substrate forhigh-precision processing of semiconductor wafers to a semiconductorwafer. On the other hand, however, it can be also used as a tackyadhesion layer of a protective tape, and excellent characteristics canbe exerted also in such a case.

According to the adhesive composition of the present invention, requiredheat resistance and stripping properties can be attained by selectingthe stripping liquid to modify the composition. More specifically,because the stripping liquid used for removing the protective substratefrom the semiconductor wafer has a solubility parameter (SP value) thatis approximate to the SP value of the acrylic polymer, more excellentstripping properties can be attained. The SP value referred to herein isa known parameter which is derived by raising the cohesive energydensity (evaporation energy of one molecule per unit area) to the ½-thpower, and represents the degree of polarity per unit volume. The SPvalue of the acrylic polymer as the adhesive composition of the presentinvention is preferably 8.8 to 9.3 (cal/cm³)^(1/2), and more preferably8.9 to 9.2 (cal/cm³)^(1/2). The stripping liquid for the adhesivecomposition in this scope is particularly preferably PGMEA (SP value:9.2) in light of the environmental burden, and stripping properties.

Although the SP value can be measured by a known method as described in,for example, Japanese Patent No. 3688702, it can be also estimated by avariety of known estimation method such as one reported by Hildebrand,Small, Foy, Hansen, Krevelen, Fedors, Hoftyzer. In many of such cases,the SP value of the acrylic polymer is represented by the weightedaverage of the SP value of the constituting monomer.

Since there is not a (meth)acrylic acid monomer in the resinconstitution of the present invention, the carboxyl group content can bekept at no greater than 1.0 mmol/g. Thus, the SP value can becontrolled, thereby capable of attaining favorable solubility to meetthe stripping liquid.

The adhesive composition of the present invention as described in theforegoing can be used in any method of: a method in which thecomposition is applied directly in the form of a liquid on the materialto be processed thereby forming an adhesive composition layer, or amethod in which the adhesive composition layer is formed and dried on aflexible film beforehand, and this film (dry film) is used afterattaching to the material to be processed (adhesive film method),deepening on the application.

Next, the adhesive film of the present invention is described below. Theadhesive film of the present invention is obtained by providing at leastthe adhesive composition layer of the present invention on a supportfilm. In use of the adhesive film, when the adhesive composition layeris further covered thereon by a protective film, the adhesivecomposition layer can be easily provided on the material to be processedby peeling the protective film from the adhesive composition layer andoverlaying the exposed adhesive composition layer on the material to beprocessed, and subsequently peeling the support film from the adhesivecomposition layer.

Use of the adhesive film of the present invention enables formation of alayer having more excellent film thickness uniformity and surfacesmoothness, as compared with the case of forming the adhesivecomposition layer by directly applying the adhesive composition on thematerial to be processed.

The support film used for producing the adhesive film of the presentinvention is not particularly limited, and any one can be used as longas the adhesive composition layer formed as a film on the support filmcan be peeled easily from the support film, and it is a mould releasingfilm that enables transfer of each layer onto the surface to beprocessed of the protective substrate, wafer and the like. Examples ofsuch a support film include flexible films composed of a film of asynthetic resin such as polyethylene terephthalate, polyethylene,polypropylene, polycarbonate or polyvinyl chloride with a film thicknessof 15 to 125 μm. It is preferable that the above support film besubjected to a mould releasing treatment if necessary so as tofacilitate the transfer.

When the adhesive composition layer is formed on the support film, theadhesive composition of the present invention is prepared, and isapplied on the support film such that the dried film thickness is 10 to1000 μm using an applicator, a bar coater, a wire bar coater, a rollcoater, a curtain flow coater or the like. In particular, the rollcoater is preferable because a film that is thick and has excellent filmthickness uniformity can be formed efficiently.

As the protection film, a polyethylene terephthalate film, apolypropylene film or a polyethylene film with a thickness of about 15to 125 μm to which silicone has been applied or burned in is suitable.

Next, the method of using the adhesive film of the present invention isdescribed below. First, the protective film is peeled from the adhesivefilm, and then the adhesive composition layer is bonded by thermocompression on the surface of the material to be processed by lappingthe exposed adhesive composition layer over the material to be processedand moving a heating roller on and over the support film. The protectivefilm peeled from the adhesive film can be reused if rolled up by asequential take-up roller and stored.

Although the adhesive composition of the present invention is used inapplications of adhesion as an adhesive composition, and is notparticularly limited, it can be suitably used as an adhesive compositionfor adhesion of a protective substrate for high-precision processing ofsemiconductor wafers, for use in adhering the protective substrate forhigh-precision processing of semiconductor wafers to a substrate such assemiconductor wafers. The adhesive composition of the present inventioncan be suitably used in the method of attaching a substrate described inJapanese Unexamined Patent Application, First Publication No.2005-191550.

Next, the method of attaching a substrate using the adhesive compositionof the present invention is described below. In detail, this methodincludes, prior to the step of grinding a substrate such as asemiconductor wafer to give a thin plate, attaching the circuit-formedsurface of the substrate to a protective substrate (support plate).According to this method, cracking and chipping of the substrate islikely to be generated when the thickness of the substrate such as asemiconductor wafer is reduced. After applying the adhesive compositionon the semiconductor wafer surface having a circuit (element) formedthereon, the fluidity of this adhesive composition is reduced bypreliminary drying, whereby the adhesive composition layer is formed.The temperature in the preliminary drying step is preferably 200° C. orlower. The preliminary drying is carried out by, for example, heating at80° C. for 5 min using an oven. The thickness of the adhesivecomposition layer is determined depending on the relief structure of thecircuit formed on the surface of the semiconductor wafer. In order toincrease the thickness of the adhesive composition layer, applicationand the preliminary drying of the adhesive composition may be repeatedmore than once. Thereafter, the protective substrate is attached to thesemiconductor wafer provided with the adhesive composition layer formedto have a predetermined thickness. When the adhesive composition isapplied onto the circuit-formed surface of the substrate such as asemiconductor wafer by a spin coater, a raised part referred to as abead portion is often formed on the periphery. In this instance, thebead portion can be removed with a solvent before the preliminary dryingof the adhesive composition. By thus carrying out the preliminarydrying, the film thickness of the adhesive composition layer can bereadily controlled.

The protective substrate is pressed against the adhesive layer tointegrate therewith, and the adhesive layer is dried concomitant with orafter completing the pressing. The temperature in this drying step ispreferably 300° C. or lower.

When the protective substrate is bonded by thermo compression to theadhesive layer, a number of through holes may be provided in thethickness direction in order to avoid remaining of bubble between theprotective substrate and the adhesive layer, or for the purpose ofinjecting the stripping liquid between the adhesive layer and theprotective substrate upon the peeling. In such a process, thepreliminary drying preferably accomplishes drying until the adhesivedoes not exude from the through hole when the pressing is carried out.

According to the adhesive composition of the present invention, thetemperature in the preliminary drying step can be 200° C. or lower (40to 200° C.), while the temperature in the drying step can be 300° C. orlower (40 to 300° C.).

As the stripping liquid for removing the adhesive composition, inaddition to the solvent for use in the adhesive composition: monovalentalcohols such as methanol, ethanol, propanol, isopropanol, or butanol;cyclic lactones such as γ-butyrolactone; ethers such as diethyl ether oranisole; dimethylformaldehyde, dimethylacetaldehyde or the like may beused. In particular, a stripping liquid including propylene glycolmonomethyl ether acetate, or ethyl lactate as a major ingredient ispreferable in light of the environmental burden and strippingproperties.

EFFECTS OF THE INVENTION

As described in the foregoing, the adhesive composition according to thepresent invention is accompanied by reduced gas generation upon heating(has low hygroscopicity), has high alkali resistance, has heatresistance of 200° C. or higher, and can be easily removed with astripping liquid. Moreover, excellent protective characteristics, andholding characteristics can be exhibited for the material to beprocessed even though the composition is used as a tacky adhesion layerof a protective sheet, not alone as a protective substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graphic representation of results of measuring TDS of thecoating film in Example; and

FIG. 2 shows a graphic representation of results of measuring TDS of thecoating film in Comparative Example.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Examples of the adhesive composition according to the present inventionare described below. The examples presented below are merely anillustration for appropriately demonstrating the present invention; andthe present invention is not any how limited thereto.

EXAMPLES Examples 1 to 11

A flask equipped with a stirrer, a refluxer, a thermometer, and adriptank was substituted with nitrogen gas, and thereafter the flask wascharged with 100 parts by mass of propylene glycol methyl ether acetate(PGMEA) as a solvent, and then stirring was started. Thereafter, thetemperature of the solvent was elevated to 80° C. Next, the driptank wascharged with various types of monomers shown in Tables 1 and 2 below ata blending ratio (parts by mass) shown in Tables 1 and 2, respectively,and the mixture was stirred until all ingredients were dissolved.Subsequently, this solution was uniformly dripped into the flask over 3hrs, then polymerization was successively performed at 80° C. for 5 hrs.The reaction solution was then cooled to room temperature to obtain anacrylic polymer of the present invention.

TABLE 1 Example 1 2 3 4 5 6 7 8 (c1) methyl 25 15 15 20 15 15methacrylate (c2) n-butyl 30 15 15 15 15 15 methacrylate (c3) ethyl 35acrylate (a) styrene 55 50 45 55 50 55 50 45 (b1) isobornyl 20 10 10 15methacrylate (b2) 20 10 10 dicyclopentanyl methacrylate (b3) cyclohexyl20 methacrylate (b4) 20 ethylcyclohexyl methacrylate (b5) 20phenoxyethyl acrylate

Comparative Examples 1 to 2

A flask equipped with a stirrer, a refluxer, a thermometer, and adriptank was substituted with nitrogen gas, and thereafter the flask wascharged with 100 parts by mass of propylene glycol methyl ether acetate(PGMEA) as a solvent, and then stirring was started. Thereafter, thetemperature of the solvent was elevated to 80° C. Next, the driptank wascharged with various types of monomers shown in Table 2 below at ablending ratio (parts by mass) shown in Table 2, respectively, and themixture was stirred until all ingredients were dissolved. Subsequently,this solution was uniformly dripped into the flask over 3 hrs, thenpolymerization was successively performed at 80° C. for 5 hrs. Thereaction solution was then cooled to room temperature to obtain anacrylic polymer of the present invention.

TABLE 2 Example and Comparative Example 9 10 11 1 2 (c1) methyl 30 6 10methacrylate (c2) n-butyl 30 15 20 methacrylate (a) styrene 25 25 90 4530 (b1) isobornyl 15 30 4 15 methacrylate (b2) dicyclopentanyl 30 10methacrylate (b3) cyclohexyl 10 methacrylate (d1) methacrylic acid 30(d2) 2-hydroxyethyl 30 acrylate

Evaluation

Each acrylic polymer (adhesive composition) of each of the aboveExamples 1 to 11 and Comparative Examples 1 to 2 was evaluated on thefollowing characteristics.

Application Property

The adhesive composition was applied on a 6-inch silicon wafer using aspinner at 1000 rpm for 25 sec, and the wafer was heated under fourtypes of heating conditions on a hot plate. In these four types of heatconditions, heating temperatures were 110° C., 150° C. and 200° C., andheating time period was 3 min. The film thickness was 15 μm. Thus formedfilm face was visually observed, and application property was evaluatedin accordance with the following evaluation standard.

◯: The obtained coating film exhibited no unevenness, and was uniform.

x: The obtained coating film exhibited unevenness such as pinhole andrepelling.

Flexibility

The presence or absence of crack on the dry coating film was visuallyobserved, and the evaluation was made in accordance with the presence orthe absence of crack on two kinds of the samples having a film thicknessof 15 μm and 20 μm. The presence of crack in both cases was graded x;the presence in the case of 15 μm-film thickness while the absence inthe case of 20 μm-thickness was graded Δ; and the absence in both caseswas graded ◯.

Heat Resistance, and Hygroscopicity

Each adhesive composition of the Examples and Comparative Examples wasapplied on a silicon wafer, and the temperature of the coating film waselevated from lower than 50° C. up to 250° C. The amount of degassingfrom the film was measured, and the evaluation was made according to theamount of degassing. For the measurement, a TDS method (ThermalDesorption Spectroscopy method; temperature-programmed desorptionanalysis method) was employed. EMD-WA1000 manufactured by ESCO, Ltd. wasused as the apparatus for determination of TDS (thermal desorptionspectrometer; emitted gas measurement device). The evaluation of theheat resistance was made to grade: ◯, when the intensity at a positionwith a temperature of 200° C. was no greater than 10000, and the residuewas not observed by a metal microscope: Δ, when the residue was notobserved by a metal microscope although the intensity was no less than10000; and x, when the intensity was no less than 10000, and the residuewas observed by a metal microscope. With respect to the evaluation onhygroscopicity, it was graded: ◯, when the intensity at a point with atemperature of 100° C. was no greater than 10000; and x, when theintensity was no less than 10000. In formation of a through electrode orthe like, the adhesive is kept in a high-temperature environment;therefore, high hygroscopicity results in vaporization of the moisture,whereby adhesion failure may be caused.

Conditions of the measurement by way of the TD spectrometer were as inthe following.

Width: 100

Center Mass Number: 50

Gain: 9

Scan Speed: 4

Emult Volt: 1.3 KV

Measurement temperature: 40° C. to 250° C.

In the measurement by way of the TD spectrometer, the coating film wasfed into the measuring chamber, and the measurement was initiated oneminute later. Graphic representations of the results of measuring TDSare shown in FIG. 1 (Example 1) and FIG. 2 (Comparative Example 1).Examples 2 to 11 also gave the results representing a shape of the graphsimilar to that shown in FIG. 1 in the range of 0 to 200° C. In thegraph, the elevated (measurement) temperature is indicated along theabscissa, while the arbitrary intensity is indicated along the ordinate.Emult Volt in the measurement conditions is an abbreviation of “ElectronMultiplyer Acceleration Voltage”, which is generally denoted as Q-mass(quadruple mass spectrometer) accelerating voltage.

Evaluation of heat resistance and hygroscopicity is enabled by thisgraphic representation on the grounds as in the following. Specifically,since the emitted gas at 100° C. or lower shall be water vapor or anazeotropic gas thereof, low value at this temperature leads to anevaluation that the moisture was not absorbed. Whereas, the emitted gasat a temperature of 100° C. or higher is any gas other than water vaporor the azeotropic gas thereof, i.e., almost a gas generated from theresin; therefore, less generation of such a gas can lead to anevaluation that less thermal degradation was caused. In particular,lower amount of the emitted gas at around 200° C. (approximate to atemperature of rising) leads to an evaluation that greater resistance tothermal degradation was suggested.

Stripping Property

The SP value of the acrylic polymer used in the adhesive composition wasestimated according to a Trouton's rule, and Hildebrand's formula. TheSP value is derived by raising the cohesive energy density, i.e.,evaporation energy of one molecule per unit volume, to the ½-th power,and represents the degree of polarity per unit volume.

The results of evaluation with respect to the aforementioned evaluationitems are presented in the following Table 3 (Examples) and Table 4(Examples and Comparative Examples).

TABLE 3 Example 1 2 3 4 5 6 7 8 Application ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ propertyFlexibility ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Heat resistance ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘Hygroscopicity ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Stripping 9.0 9.0 9.1 9.0 9.1 9.0 9.0 8.9property (SP value)

TABLE 4 Example and Comparative Example 9 10 11 1 2 Application property∘ ∘ ∘ ∘ ∘ Flexibility ∘ ∘ Δ ∘ ∘ Heat resistance Δ Δ ∘ x x Hygroscopicity∘ ∘ ∘ x x Stripping property 8.9 8.6 9.2 9.7 9.5 (SP value)

INDUSTRIAL APPLICABILITY

As described hereinabove, the adhesive composition and the adhesive filmaccording to the present invention are accompanied by reduced gasgeneration upon heating (has low hygroscopicity), has high alkaliresistance, has heat resistance of 200° C. or higher, and can be easilyremoved with a stripping liquid. Moreover, excellent protectivecharacteristics and holding characteristics can be exhibited for thematerial to be processed even though they are used as a tacky adhesionlayer of a protective sheet, not alone as a protective substrate.

1. An adhesive composition comprising as a major ingredient, an acrylicpolymer produced from (a) styrene, (b) a (meth)acrylic ester monomercontaining a cyclic skeleton, and (c) an alkyl (meth)acrylate monomer.2. The adhesive composition according to claim 1 wherein the(meth)acrylic ester monomer containing a cyclic skeleton (b) comprisesat least (b1) a (meth)acrylic ester monomer containing a cyclic skeletonhaving a substituent on the cyclic skeleton, and (b2) a (meth)acrylicester monomer containing a cyclic skeleton not having a substituent onthe cyclic skeleton.
 3. The adhesive composition according to claim 1wherein the acrylic polymer has a carboxyl group content of no higherthan 1.0 mmol/g.
 4. The adhesive composition according to claim 1, whichis an adhesive composition for adhesion of a protective substrate forhigh-precision processing of a semiconductor wafer used for adhering aprotective substrate for high-precision processing of the semiconductorwafer to the semiconductor wafer.
 5. The adhesive composition accordingto claim 4 wherein a stripping liquid used for removing the protectivesubstrate from the semiconductor wafer has a solubility parameter (SPvalue) that is approximate to the SP value of the acrylic polymer.
 6. Anadhesive film comprising an adhesive composition layer formed from atleast the adhesive composition according to claim 1 on a support film.